Accuracy fuze for airburst cargo delivery projectiles

ABSTRACT

In one aspect, an artillery projectile apparatus is provided that includes a carrier projectile containing a payload, and a fuze disposed at an ogive of the projectile and which is configured to eject the payload when the fuze is detonated. The fuze includes a receiver configured to receive location information from a radionavigation source and a processor configured to acquire position data from the receiver. The processor is also configured to estimate a projectile flight path using the position data, to determine intercept parameters of the artillery projectile relative to an ejection plane of its payload cargo, and to adjust an ejection event initiation command time of the payload in accordance with the determined intercept parameters. In some configurations, the present invention dramatically decreases range errors typically associated with delivering artillery payloads to specific targets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/368,112 filed on Feb. 18, 2003. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a low cost munition fuze havingincreased accuracy, and more particularly to a low cost munition fuzehaving reduced projectile launch and flight errors.

BACKGROUND OF THE INVENTION

Studies performed on the long-range accuracy of the current U.S. Armyartillery shell stockpile have suggested that at ranges above 20kilometers, numerous rounds must be fired to achieve a lethal effect onthe target. Area saturation can be used to defeat or immobilize atarget, at the costs of delaying advancing troops from reaching thetarget and allowing an enemy some opportunity to evade an assault.Additionally, conventional munition inaccuracies require friendly firetarget standoff distances of greater than 600 meters, which preventssuppressive fire in support of target engagement by advancing troops foras much as 20 minutes.

Precision weapons are being developed to increase range, tosignificantly reduce the conventional munition logistic task and toresolve the battle engagement time and mobility issues. However,precision weapons are expensive, and their high accuracy may not berequired for conventional munition ranges.

SUMMARY OF THE INVENTION

Some configurations of the present invention therefore provide anartillery projectile apparatus that includes a carrier projectilecontaining a payload, and a fuze disposed at an ogive of the projectileand which is configured to eject the payload when the fuze is detonated.The fuze includes a receiver configured to receive location informationfrom a radionavigation source and a processor configured to acquireposition data from the receiver. The processor is also configured toestimate a projectile flight path using the position data, to determineintercept parameters of the artillery projectile relative to an ejectionplane, and to adjust an ejection event initiation command time of thepayload in accordance with the determined intercept parameters.

Various configurations of the present invention also provide a methodfor delivering an artillery projectile payload to a target. The methodincludes determining a cargo ejection plane between a gun firing theartillery projectile and the target and a nominal ejection eventinitiation command time to deliver the artillery projectile payload tothe target; firing the artillery projectile at the target; acquiring, atthe artillery projectile after firing, position and time data; andadjusting, at the artillery projectile after firing, ejection eventinitiation command time of the artillery projectile payload inaccordance with the acquired position and time data.

Some configurations of the present invention also provide a fuze thatincludes a fuze housing; fuze electronics including a processor and aradionavigation receiver contained within the fuze housing; and a powersupply configured to power the processor and the radionavigationreceiver; an explosive charge responsive to the processor. The processoris responsive to the radionavigation receiver to adjust a time at whichthe explosive charge is detonated.

It will be observed that configurations of the present invention providea more accurate alternative to conventional munitions systems and a lessexpensive alternative to precision munitions systems. In someconfigurations, the present invention contains the artillery fuzefunctions, is profile-interchangeable with NATO requirements as definedin MIL-Std-333B, and/or incorporates technologically available smartmunition updates.

Furthermore, it will be observed that some configurations of the presentinvention provide low cost, mid-range accuracy improvements that canreduce the number of deployed projectiles needed to acquire a target.Some configurations also provide additional cover fire protection toadvancing troops by reducing standoff distances and times owing toimproved munition accuracies.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional drawing representative of variousconfigurations of an artillery projectile of the present invention.

FIG. 2 is a partial cross-sectional drawing representative of variousconfigurations of a fuze of the present invention, including a fuzeconfiguration suitable for use in configurations of the artilleryprojectile represented in FIG. 1.

FIG. 3 is a drawing showing the relationship of various trajectories andejection points relative to a nominal cargo ejection plane and a target,where the trajectories intercept the nominal cargo ejection plane atdifferent heights.

FIG. 4 is a drawing showing the relationship of various trajectories andejection points relative to a nominal cargo ejection plane and a target,where the trajectories intercept the nominal cargo ejection plane atdifferent angles.

FIG. 5 is a drawing indicating the increased payload delivery accuracyachievable by various configurations of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

In some configurations and referring to FIG. 1, the present inventioncomprises an artillery projectile 10 that comprises a conventionalcarrier projectile 11 having a front head part or ogive 12 and a rearbase part 14. Carrier projectile 11 contains one or more payloads suchas grenades 18 that are configured to detonate on a target. A fuze 22 isdisposed at ogive 12 and is configured to eject the payload when fuze 22is detonated. In particular, when fuze 22 is detonated, an expanding gasfills a cavity 24 and forces piston 26 to press plate 28 rearward,forcing payload or payloads 18 to push against base 14. Base 14 is thusforced off carrier projectile 11 and payload or payloads 18 are ejectedfrom projectile 11. Payload(s) 18 are spin-deployed to control payloaddispersion during delivery. The operation and construction of piston 26,plate 28, payload 18 and base 14 are conventional and need not bedescribed further.

Referring to FIG. 2, fuze 22 comprises an outer casing 30, a fuze settercoil 32, circuit cards 34, a power supply assembly including a battery38, a safe and arm assembly 40, and a booster cup 42. A lead charge 44is configured to detonate booster pellets 46 in booster cup 42 inresponse to an ejection command from a processor 48 residing on circuitcards 34. For safety, the ejection command is preceded by two sensedlaunch commands in addition to an adjusted firing time command from theprocessor. Fuze 22 in some configurations is interface-equivalent withMIL-Std-333B specifications. Fuze 22 has screw threads 52 for attachmentat ogive 12 of projectile 11.

In some configurations, a global positioning satellite (GPS) receiver 50is provided in fuze 22 to reduce range errors. Receiver 50 utilizes aring antenna 36 encircling fuze 22 to receive signals from GPSsatellites (not shown). In another embodiment, another GPS-receptiveantenna suitable for use with a high-spin-rate projectile could be used.Received GPS data from receiver 50 and time are used by processor 48 todetermine a flight trajectory and to adjust payload ejection eventinitiation command timing for increased range accuracy, for example, byreducing the effects of temperature, gun lay, launch, firing charge,baseburner and projectile flight range errors. In some configurations,to avoid loss of a projectile, processor 48 defaults to a basic M762fuze mode with fixed ejection times in the event of a GPS subsystemanomaly, such as jamming, inability to acquire satellite transmissions,etc.

Under normal conditions, GPS data will be available, and onboardprocessor 48 will use time data and the acquired GPS position data tocalculate a projectile flight path, and to predict an intercept angle,height and time at which artillery projectile 10 will pass through a gunand target-defined ejection plane 62, as represented in FIG. 3.Downrange distance traveled by the payload 18 from an ejection point isa function of the height or elevation of the ejection point. Adifference between an actual intercept point and a nominal interceptpoint 64 of a nominal projectile flight path 68 is determined andutilized to adjust an ejection event initiation command time forejecting cargo payload (e.g., grenade or other dispensable munitions18). For example, if artillery projectile 10 is more energetic thannominal, it would follow a flight path such as flight path 72. In thiscase, the ejection event initiation command time is adjusted so thatejection occurs at a point 74 prior to interception of cargo ejectionplane 62 and payload 18 follows path 78, rather than path 66, to target60. If the projectile is less energetic than nominal, the ejection eventinitiation command time is adjusted to eject payload 18 at a point 76after interception of flight path 70 of artillery projectile 10, andpayload 18 follows path 80 to target 60. These timing adjustments thuseffect a more accurate delivery of payload 18 to target 60.

In some configurations, a secondary range adjustment is made bycorrecting the ejection event initiation command time of payload 18 inaccordance with the trajectory slope. More particularly, and referringto FIG. 4, if the actual trajectory slope 84 is steeper and the forwardor downrange velocity of the cargo at ejection is less than would be thecase with a nominal trajectory slope 68, ejection event initiationcommand time is delayed so that payload 18 will impact target 60 byejecting payload 18 at ejection point 86 and payload 18 follows descentpath 92. On the other hand, if the actual trajectory slope 82 is flatterthan nominal trajectory slope 68, the payload will be travelingdownrange faster after release than if the payload were followingnominal slope 68. Therefore, the ejection event initiation command timeis advanced so that ejection of payload 18 occurs at a point 88 beforetrajectory slope 82 intersects cargo ejection plane 62. Payload 18 thusfollows a path 90 that allows the payload to travel farther downrangeafter ejection, and yet still hit at or near target 60.

Referring to FIG. 5, by providing a fuze with a first order, or low costone-dimensional range correction, a footprint representing typicaldelivery errors to a target 60 is reduced from a footprint 56representing typical delivery errors in the absence of correction to areduced size footprint 58 representing the delivery errors of aplurality of artillery projectile configurations and delivery methodconfigurations of the present invention. Configurations of the presentinvention can be utilized in conjunction with techniques for reducingdeflection errors to effect a two-dimensional correction and thusprovide additional accuracy.

In some configurations of the present invention, power consumption isreduced by increasing the interval between GPS data samples. Thesampling intervals can pre-selected in accordance with desired accuracyand power consumption levels, or may be varied during flight in someconfigurations to obtain a satisfactory trade-off between accuracy andpower consumption. Estimated projectile flight parameters may beutilized to adjust GPS sampling intervals. For example, some 60-secondprojectile flights may require between 6 to 10 samples to adequatelyestimate the ejection time and trajectory intercept, although the numberof samples required may vary from flight to flight.

Some configurations of the present invention utilize the following stepsto hit a target with artillery projectile 10. First, using spatialposition finding devices, both the target and the artillery projectilefiring gun are located in three-dimensional space. The fuze power onsequence is then initiated. GPS gun and target location data and basicfuze initialization data is input to the fuze using the fuze setter. Atypical configuration would accommodate turn-on, system initialization,and data entry and/or update within twenty minutes of the projectilefiring.

An onboard processor 48 establishes, using target location data inputs,a cargo ejection plane 62 that is perpendicular to an azimuth range linebetween the gun and target 60. Cargo ejection plane 62 is located uprange from target 60 by a distance determined to cause the deployedcargo grenades 18 to land on the target when cargo grenades 18 aredispensed from a nominal flight performance projectile 68. For example,in some configurations, a nominal projectile flight path 68 interceptscargo ejection plane 62 at a nominal flight path to ejection planeintercept angle estimated at 52 degrees and at an estimated nominalheight of burst altitude of 500 m. Initially, processor 48 is programmedto utilize data from GPS receiver 50 of fuze 22 to eject payload 18 whenprojectile 10 Intercepts ejection plane 62. In some configurations, theinitialized intercept time is the same as the basic M762 set time, andfurther the processor 48 is configured to use the initialized intercepttime as a default ejection event initiation command time in the event ofa GPS anomaly or a fuze processing anomaly, thereby avoiding loss of theprojectile.

After the fuze is programmed with target and gun location data, theartillery projectile 10 is loaded and fired. During flight, GPS receiver50 acquires position and time data. Processor 48 is configured to useacquired GPS data to determine a deviation for a nominal projectileflight path to predict an intercept angle, height and time at whichprojectile 10 will pass through ejection plane 62. As the flight ofprojectile 10 continues, ejection plane intercept parameters are updatedwith each new GPS data set. A convergence test, for example, can beperformed following each new set of intercept information to determineif a GPS anomaly has occurred. A detected GPS anomaly causes processor48 to default to either the last predicted set of ejection planeintercept parameters or to a typical conventional fuze set time.Processor 48 is configured to use either the last predicted ejectionplane parameters or a typical conventional fuze set time, dependent uponthe number of successful GPS updates before an anomaly occurs, in theevent such an anomaly occurs prior to ejection.

In some configurations, the intercept point of projectile 10 withejection plane 62 can be predicted to an altitude of plus or minus 12 mand a range of plus or minus 8 m. Once the ejection plane interceptpoint is determined, a difference between the nominal impact point and apredicted impact point is used to enhance accuracy by adjusting theejection event initiation command time. For example, if the predictedejection plane 62 intercept point and time and nominal impact point 64and time are coincident then no correction to the ejection eventinitiation command time is made and a nominal grenade decent trajectory66 is used for the payload or grenades 18 to impact target 60. However,if artillery projectile 10 has higher velocity than a nominal artilleryprojectile, the predicted cargo ejection plane 62 intercept point 94will be higher than nominal cargo ejection intercept point 64. Based onan elevation difference between cargo ejection intercept points 64 and94 and a difference between times corresponding to points 64 and 94, theejection event initiation command time is reduced, thus moving theejection point up range to a point 74 and thereby adjusting payload 18impact point to more closely coincide with target 60. Similarly, ifartillery projectile 10 has lower velocity than a nominal artilleryprojectile, the ejection event initiation command time is increased sothat the payload or grenades 18 are ejected at point 76 rather than atpoint 96, thereby adjusting descending grenade 18 to impact the groundat a point closely coinciding with target 60.

In some configurations, and referring to FIG. 4, a secondary range erroradjustment is made by correcting the payload ejection event initiationcommand time for the artillery projectile trajectory intercept angle andtime with cargo ejection plane 62. In this case, if projectile intercepttrajectory 84 is steeper than nominal intercept trajectory 68, the cargoejection event initiation command time, i.e. the intercept trajectory 84time, is delayed to allow payload 18 to fly further down range beforeejecting its payload at a point 86. This adjustment allows the grenadesto impact the ground at the target range. Similarly, if projectileflight trajectory 82 is flatter than nominal intercept trajectory 68,the timing is advanced to eject the payload or grenades 18 at point 88,prior to interception of ejection plane 62 by trajectory 82.

In some configurations, the fuze 22 design may meet some or all of thefollowing specifications:

NATO Fuze Configuration, MII-Std-333B

Mil-Std-1316D with overhead safety (Arm 50-msec. prior to CargoEjection)

M762S&A

Inductive set only with EPIAS (No hand set or adjustment)

20 minute ground set capability (No 10 day preset)

XM982 GPS jamming protection

M762 timing is default mode

Flight time 100 sec.

Accuracy 125 m circular error probability (CEP) at 35 km with 2 hr. met.Data

No decrease in lethal area

Gun harden—20,000 g setback

Gun harden—20,000 rpm spin

20 year shelf life

In some configurations, the profile of fuze 22 is identical to the M762profile and satisfies the NATO requirements as defined in Mil-Std-333B.The front end of fuze 22 incorporates the same plastic ogive and fuzesetter coil 32 that is used on some conventional configurations of M762fuzes. The base of fuze 22 also retains the basic M762 design. Boostercap 42 includes explosives 46, and lead charge 44. Safe and arm assemblyand piston actuator 40 prevents arming until artillery projectile 10 iswithin 50 msec. from payload 18 ejection.

Unlike conventional M762 fuzes, GPS receiver 50 with ring antenna 36 maybe provided on circuit boards 34 in fuze 22 and processor 48 may beconfigured to take advantage of the information received by receiver 50.In some configurations, a battery 38 is provided to power fuzeelectronics, including GPS receiver 50 and processor 48.

Some configurations of fuze 22 utilize three double-sided circuit boards34, which provide 16 square inches of component mounting surface. GPSreceiver 50 and trajectory analysis processor 48 require approximately10 square inches of circuit board area. Addition fuze electronics oncircuit boards 34 utilize the GPS receiver clock and therefore thesafety functions and firing circuits can be accommodated on 3 additionalsquare inches of circuit board. Thus, up to three square inches can beprovided for additional circuitry and functionality, if required.

Battery 38 can provide power for driving GPS receiver 50, processor 34and additional fuze circuitry for 20 minutes of ground time followed a2-second power initialization spike and then a constant power drain fora 100-second flight period. A battery with a volumetric configuration of1.5 inches in diameter by 0.88 inches high has sufficient capacity insome configurations, although other battery configurations may also beused, depending upon cost and performance requirements.

The center section of the configurations of fuze 22 represented by FIG.2 feature axial conformal circuit boards 34 mounted in front of battery38. The battery can be, for example, a right circular cylinderpositioned between safe and arm assembly 40 and circuit boards 34. Otherconfigurations feature forward or aft mounting locations for battery 38.Some configurations provide stacked round circuit cards 34 instead ofthe conformal axial circuit boards 34 shown in FIG. 2. A battery 38 andcircuit card 34 configuration can be selected in accordance with dynamicenvironment survival vs. assembly ease and component costs requirements.

It will be thus observed that configurations of the present inventionprovide a more accurate alternative to conventional munitions systemsand a less expensive alternative to precision munitions systems. Theabove-described fuze provides improved accuracy without depleting thespin of a deployed cargo. Because deployment spin is conserved, ahistorical footprint of the cargo can be preserved. Also, someconfigurations are profile-interchangeable with the M762 fuze perMIL-Std-333B specifications and some configurations incorporatetechnologically available smart munition updates.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method for delivering an artillery projectile payload to a target, said method comprising: determining a cargo ejection plane between a gun firing the artillery projectile and the target and a nominal ejection event initiation command time to deliver the artillery projectile payload to the target; firing the artillery projectile at the target; acquiring, at the artillery projectile after firing, position and time of flight data of said projectile; using derived position data and time of flight data to predict a time of intercept and altitude; and adjusting, at the artillery projectile after firing, ejection event initiation command time of the artillery projectile payload in accordance with the acquired position and time data.
 2. A method in accordance with claim 1, wherein said acquiring position and time data comprises receiving global positioning satellite (GPS) data using a receiver located at the artillery projectile.
 3. A method in accordance with claim 1, further comprising sampling said GPS data at a variable rate during flight.
 4. A method in accordance with claim 1, wherein said receiving GPS data further comprises utilizing an antenna for a high-spin-rate projectile.
 5. A method in accordance with claim 1, wherein said adjusting ejection event initiation command time comprises adjusting the ejection event initiation command time utilizing a processor at the artillery projectile.
 6. A method in accordance with claim 1, further comprising updating nominal ejection plane intercept parameters following acquisition of a GPS data set.
 7. A method in accordance with claim 6, further comprising performing convergence tests on the updated ejection plane intercept parameters following acquisition of a GPS data set.
 8. A method in accordance with claim 7, further comprising conditioning said adjusting the ejection event initiation command time upon results of the convergence tests, and utilizing a default ejection event initiation command time in the event that the convergence tests indicate a GPS anomaly.
 9. A method in accordance with claim 1, wherein said adjusting ejection event initiation command time of the artillery projectile payload comprises predicting an elevation and time for the artillery projectile to intercept the ejection plane and reducing said predicted time if an ejection plane interception point is higher than a determined nominal intercept point, and increasing said predicted time if the ejection plane interception point is lower than the determined nominal intercept point. 